1. Field of the Invention
The present invention relates to a scan method of a capacitive touch device, and more particularly to a clustered scan method of a capacitive touch device.
2. Description of the Related Art
Current capacitive touch devices usually have two types of scan methods, namely, self-capacitance scanning method and mutual-capacitance scanning method. Various types of mutual-capacitance scanning methods have been developed and dedicated for different demands of capacitive touch devices. Clustered scan method pertains to one type of mutual-capacitance scanning methods. Exemplified below are several examples of the clustered scan method.
As disclosed in U.S. Pat. No. 7,812,827, a simultaneous sensing arrangement technique is applied to a capacitive touch device with multiple sensing points intersected by multiple drive lines and multiple sense lines. Such technique can enhance operation of multi-touch sensing configuration by simultaneously driving multiple rows of drive lines of the capacitive touch device. With reference to FIG. 9A, given 16 drive lines X0˜X15 as an example, the drive lines can be classified into four groups, that is, groups 1˜4. Each group includes four drive lines. With reference to FIG. 9B, a clustered scan method disclosed by the US patent simultaneously outputs two driving signals 801, 802 to the drive lines in the groups 1 and 2, and sensed values corresponding to the stimulated drive lines are represented by signals X0, X1. As the two driving signals have four in-phase pulses heading in a time duration T1 and four pulses mutually phase-shifted by a 180 degrees trailing in a time duration T2, the sensed values in the time durations T1 and T2 can be considered as (X0+X1) and (X0−X1).
Likewise, the sensed values corresponding to the drive lines in groups 3 and 4 in time durations T3 and T4 are (X2+X3) and (X2−X3) respectively after two driving signals 806, 807 are applied to the drive lines. By sending driving signals to all the drive lines of each non-overlapped group and varying phases of driving signals, inputs done by finger touch can be preliminarily determined by a combined result of the sensed values X0˜X3.
Disclosed by US Patent Publication No. 2013/0271410 and applied to an integrated type of liquid crystal display (LCD) touch display of a capacitive touch device, another clustered scan method primarily perform scanning using driving signals with different frequencies first, and then determines a noise value under each driving signal. The lower the noise value is the lower noise of a corresponding driving signal is. Those driving signals with relatively low noise are used to perform scanning.
With reference to FIG. 10, in steps 4 to 19, a vertical blank interval (VBI) of an LCD display device is used for scanning 15 drive lines. Three driving signals with different frequencies A to C are applied to the 15 drive lines in steps 4 to 7. The driving signal with the frequency A is simultaneously applied to the drive lines indicated by R0, R4, R8 and R12. The driving signal with the frequency B is simultaneously applied to the drive lines indicated by R1, R5, R9 and R13. The driving signal with the frequency C is simultaneously applied to the drive lines indicated by R3, R7, R11 and R14. All the rest of the drive lines are not driven.
In steps 8 to 11, the foregoing three driving signals are simultaneously applied to the drive lines next to the drive lines driven in steps 4 to 7 again. In other words, the driving signal with frequency A is simultaneously applied to the drive lines indicated by R1, R5, R9 and R13, the driving signal with frequency B is simultaneously applied to the drive lines indicated by R2, R6, R10 and R14, the driving signal with frequency C is simultaneously applied to the drive lines indicated by R4, R8 and R12, and the rest of the drive lines are not driven. The three driving signals are repeatedly applied in a similar fashion until the scanning process from steps 4 to 11 can be carried out four times. During each scanning process, the phases of the frequencies A, B, C of the driving signals can be further changed and marked by -A, -B and -C. Hence, the use of driving signals with different frequencies and phases can increase the scanning speed and provide better signal-to-noise ratio (SNR).
To cope with the issue of unsatisfactory SNR, US Patent Publication No. 2013/0057490 discloses a technique pertinent to “signal-to-noise ration in touch” to increase SNR and measurement accuracy of a signal generated by touch event or an approaching touch object. With reference to FIG. 11, the technique involves simultaneous application of driving signals 410A, 410B to two drive lines X0, X1. Given four drive lines X0˜X3 as an example, consecutive twos of the drive lines (X0, X1), (X1, X2), (X2, X3) are sequentially driven. Suppose that the voltage level of the driving signals 410A˜410G is identical to that of the driving signal driving only one drive line. When two drive lines are driven at the same time, a sensing value of a corresponding sense line is doubled. Hence, the SNR increases. However, despite the disclosure of simultaneously driving two, three or four drive lines for the purpose of higher SNR, this technique fails to point out how bordering sense lines should be driven when multiple drive lines are simultaneously driven. For example, if there are n sense lines, when two drive lines are simultaneously driven, the sensing values of non-bordering sense lines, such as the second sense line to the (n−2)th sense line, may be as twice as the sensing value of the bordering sense line, such as the first sense line or the last sense line. False touch determination may arise from uneven distribution of the sensing values of all the sense lines.
From the foregoing examples of the clustered scan method, the clustered scan method is rather common to touch devices. Different clustered scan methods are addressed for corresponding touch devices and technical issues thereof to be resolved.
The multi-point positioning means of conventional capacitive touch sensing circuits takes an approach of driving the drive lines in X axis and measuring the sense lines in Y axis, or driving the drive lines in Y axis and measuring the sense lines in X axis. Sensors are formed by mutual capacitor that are generated between points intersected by X axis and Y axis. When a driving signal with a positive-voltage waveform or a negative-voltage waveform is used to drive a drive line, besides a mutual capacitor generated between the drive line and each intersected sense line, a self capacitor is generated between the drive line and a touch object like a finger when the finger approaches the drive line. However, if the finger and the touch device are not well-grounded, the sensors are susceptible to such self capacitor and the capacitance values measured from the mutual capacitors fails to reflect their true values due to their interaction with such self capacitor. Such inaccuracy upon measuring capacitance values is worsened when the measuring system and the human body are not well-grounded.